[PPT] - Database-Powered Web Servers Alexandros Labrinidis Univ. of PowerPoint Presentation

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Database-Powered Web Servers

Alexandros Labrinidis

Univ. of Pittsburgh

labrinid@cs.pitt.edu

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Examples of db-powered web sites

Google.com (search engine) Amazon.com (shopping) eBay.com (auctions) WellsFargo.com (online banking) weather.com (forecasts) expedia.com (travel) NSF.gov (proposal submission) my.yahoo.con (personalized newspaper) NYTimes.com (electronic newspaper)

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Motivating Example: nytimes.com

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Why is WebDB so popular?

Arguments from web “producers”:

easy to “publish” databases over the Web wealth of information available enable personalization allow targeted advertising

Arguments from web “consumers”:

no need to install special software easy to learn - uniform user interface personalized content

Today – even seemingly static sites have WebDB

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Typical WebDB architecture – 3 tiers

Web server: handle HTTP requests Application server: web workflow DB server: data storage & queries

User 1 User 2 User 3 User … User n

internet web server app server db server

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Typical WebDB architecture – 2 tiers

2-tiers: incorporate application server within web server

User 1 User 2 User 3 User … User n

internet web & app server db server

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

HTTP: HyperText Transfer Protocol

Client request:

nitrogen{ 4} telnet www.google.com 80 Trying 216.239.37.101... Connected to www.google.com. Escape character is '^ ]'. GET /index.html HTTP/1.0 [two carriage returns]

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

HTTP: HyperText Transfer Protocol

Server response:

HTTP/1.0 200 OK Content-Length: 2532 Connection: Close Server: GWS/2.0 Date: Thu, 07 Nov 2002 16:57:59 GMT Content-Type: text/html Cache-control: private Set-Cookie:

PREF= ID= 24bce47555c1db8b:TM= 1036688279:LM= 1036688279:S= t4XqRr3VPTPwK MEp; expires= Sun, 17-Jan-2038 19:14:07 GMT; path= /; domain= .google.com

< html> …. < /html> Connection closed by foreign host.

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

HTML: HyperText Markup Language

page wrapped in < html> < /html> many formatting commands:

< font color= “red”> SOMETHING IN RED< /font> CSS: Cascading StyleSheets

Form example:

<form action=“/activate.cgi” method=POST> Please give your name: <input type=text name=“username” size=15 maxlength=30> <input type=submit value=“Submit Name”> </form>

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

CGI: Common Gateway Interface

Introduced in the early 90s
Protocol for exchanging form data between

client and server

User requests form Web Server sends form to user User submits form CGI forwards form data to application process data & generate output Web Server sends

utput to user

User receives output network db server

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

CGI encoding

method= GET

Form data are encoded as part of the URL

(e.q. http://www.google.com/search?q=cmu)

method= POST

Form data are passed via environment variables

encoding of query string:

(name,value) pairs from FORM name1= value1&name2= value2&… space +

ther controls characters in hexadecimal format

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Cookies

HTTP is connection-less

a new connection is established with every request HTTP/1.1 supports persistent connections (but not popular)

Q: How to maintain state over a session? A: Cookies Cookies are text-only strings that are stored at the

browsers’ memory (and disk)

.google.com TRUE / FALSE 2147368447 PREF

ID=0a2612f3162aa05f:TM=1035999053:LM=1035999053:S=ko0- i9cOsU6nMaW6

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Cookies and Databases

Use cookie to store client-ID Storing client-ID enables personalization

Example: NYTimes.com

Storing client-ID enables access to restricted areas

Example: NYTimes.com (subscription-based access to articles)

Use cookie to prohibit duplicate submissions on polls

Randomly generated ID Matched against database of those already “voted”

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Cookies and Privacy

Cookies only store text-strings given by servers

Include domain, expiration date, etc

Only a server from the same domain can access a

previously stored cookie

The case of Doubleclick:

Same cookie used by an advertising agency Match individuals with browsing profiles that span multiple sites Huge data mining opportunity Huge controversy

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Client-side programs

Extend web user interface by running programs at clients

Allow for sophisticated UIs Must be careful of malicious code (from untrusted servers)

Java

Full-fledged programming language Protection capabilities

Other client-side scripting languages:

JavaScript (SUN) VBScript (MSFT) Flash/Shockwave (Macromedia)

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Server-side programs

Implement server applications and workflow

Programs that generate HTML Embedded HTML

Java:

Servlets Java Server Pages (JSP – SUN)

Server-side scripting:

Active Server Pages (ASP – MSFT) PHP mod_perl

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Embedded HTML: PHP

PHP stands for “PHP Hypertext Processor” http://www.php.net Example:

<html> <head> <title>Example</title> </head> <body> <?php echo "Hi, I'm a PHP script!"; ?> </body> </html>

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Generating HTML: mod_perl

mod_perl: efficiently use perl to generate HTML http://perl.apache.org Example:

#!/bin/perl print << EOF; <html> <head> <title>Example</title> </head> <body> Hi, I was generated by mod_perl! </body> </html> EOF

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

DB interface: mod_perl

Two modules – allow for portability:

DBI: database independent library DBD: database dependent driver

Example:

use DBI; my $dbh = DBI->connect(“oracle”, “user”, “pass”); my $stmt = $dbh->prepare(“SELECT * from foo;”); $stmt->execute(); while (@row = $stmt->fetchrow_array() ) { print “Row: @row\n”; } $dbh->disconnect();

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Improving Performance: CGI

CGI forks new process on every call

context switch re-connect to db server

mod_perl: maintain pool of processes

no context switch – assign call to existing process scales better – 10 times faster

[Labrinidis & Roussopoulos, SIGMOD Record, Mar 2000]

mod_perl: re-use db connections

no need to re-connect to db server twice faster than mod_perl

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Alexandros Labrinidis, Univ. of Pittsburgh

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CMU . CS 415 . 07 November 2002

Improving Performance: Caching

Web Caching

store static content close to the users avoid re-transmitting over the network consistency: Time-To-Live (TTL)

Dynamic Web Caching

store dynamic content (from db) and re-use if possible avoid re-computing from database what to cache:

entire web pages query results HTML fragments